Davide Mendolia wrote in to let me know about a new site he's started to gather as much information about continuous integration in PHP into once place as he can - PHP-CI.net.

The goal of this website is to provide information for doing continuous integration in PHP and also hosting of continuous integration process for open source software. [...] On this site you will find information about continuous integration in PHP, be able to ask an hosting of your project and consult the result of the execution of builds of project hosted.

You can also check out the blog for the project to get the latest updates on hosted projects (like their first - PHPIDS) and the Google Group he's set up for discussion.